(Not Applicable)
(Not Applicable)
The present invention relates generally to sandwich panels and, more particularly, to a sandwich panel structural joint.
Sandwich panels are increasingly used in aerospace products such as aircraft, helicopters, and spacecraft due to their desirable strength, weight, and stiffness characteristics. Sandwich panels are typically comprised of a panel core body having opposing first and second panel sides with at least one panel facesheet attached to the panel core body adjacent the first panel side. In this regard, a sandwich panel is a layered construction formed by bonding at least one or, more typically, two thin panel facesheets to the thicker panel core body. A sandwich panel is of a stressed skin type of construction in which the facesheets resist all, or nearly all, of the applied edgewise loads and planar bending moments. The spacing between the thin facesheets provides all, or nearly all, of the bending rigidity to the sandwich panel construction. The core body spaces the facesheets and transmits shear loads between them so that they are effective about a neutral axis. The core body also provides most of the shear rigidity of the sandwich panel construction. Proper choice of materials for the facesheets and the core body results in a sandwich panel construction with a high ratio of stiffness to weight. Sandwich panels must be joined to provide stiff frames capable of handling the high stresses typical of aerospace fight vehicles. The sandwich panel joints must be capable of handling bending moment, shear, tension and compression stresses.
In addition, the sandwich panel joints in spacecraft can also serve a secondary purpose in aiding in the dissipation of excess heat generated by instrumentation mounted in the interior of the spacecraft. As an aid to the active cooling system common to many spacecraft, heat can be conducted to the spacecraft exterior from the sandwich panels upon which the instrumentation and electronics are mounted. However, sandwich panels do not readily conduct heat across the core body to the exterior because the core body is generally constructed of a cellular material. Therefore, it is highly desirable to have a sandwich panel joint configuration that can assist in the conduction of heat from the interior facesheet upon which instrumentation is mounted to an exterior facesheet of an adjacent panel.
Prior art approaches for sandwich panel joint configurations are numerous. For example, the prior art describes a sandwich panel structural member which includes an integrally formed joint-forming edge structure. The joint-forming edge structure is adapted to be bonded to a complementary integrally formed joint-forming edge structure, such that the joining of any two sandwich panel structural members with the same edge structure requires no separate joining members to assist in the handling of joint loads. Each joint-forming edge structure includes a flange that extends from the sandwich portion of the sandwich panel, a web that extends from one panel skin to the other, and a flange-receiving portion integrally formed with and extending inward from the joint edge. Although this joint configuration has the benefit of accommodating any panel having the same integral edge configuration, the drawbacks are that it requires many additional joint structural members that must be laid up over the entire edge portion of each panel, necessitating special edge tooling and increasing the manufacturing cost and complexity.
The prior art also describes a sandwich panel construction utilizing a single piece of folded thermoplastic-composite-skinned, honeycomb-cored sandwich panel utilizing minimum edge-margin mortise and tenon joint corner structure. Formed by folding the single piece of sandwich panel material into a locking open box type structure, the sandwich panel structure contains interlocking joints characterized as mortise and tenon joints. End panels are folded up from the sides of a bottom panel to form side walls. Tenons extend from the margins of the right and left end panels. Mortise packets are formed in the side margins of the upper panels. The mortises and tenons create interlocking mortise and tenon joints, requiring no additional joint members. The manufacturing advantages of this sandwich panel structure are that it is constructed of one piece and is essentially self-tooling in that it has interlocking joints requiring no adhesive. However, the drawback of this configuration is that it is incapable of handling high loading conditions often encountered in aerospace flight vehicles.
Also included in the prior art is a composite sandwich panel joint comprising a first and second article. The first and second articles each include a filler layer disposed between a first and second composite layer. An end section of the first article""s first composite layer is disposed external to, overlapping and bonded to an end section of the second article""s first composite layer to form a first overlap. An end section of the second article""s second composite layer is disposed internal to, overlapping and bonded to an end section of the first article""s second composite layer to form a second overlap. The first overlap is displaced across the thickness and along the length of the joint from the second overlap. Loads are transferred across the joint from first layer to first layer and from second layer to second layer. Although this configuration has improved ability to withstand axial and bending loads, it has drawbacks in that it is complex and has a lengthy manufacturing time due to the additional joint members that must be concurrently laid up and co-cured over the entire edge of each panel.
As can be seen, there is a need for a sandwich panel joint configuration for a sandwich panel structure that is capable of providing an efficient load path across adjacent sandwich panel. Also, there is a need for a sandwich panel joint configuration that is of simple construction with a minimal number of parts. Furthermore, there is a need for a sandwich panel joint configuration with improved heat conduction capabilities across adjacent composite panels. Finally, there is a need for a simple sandwich panel joint configuration that easily connects sandwich panels having substantially differing thicknesses.
The present invention specifically addresses and alleviates the above referenced deficiencies associated with sandwich panels. More particularly, the present invention is an improved sandwich panel joint configuration.
In accordance with an embodiment of the present invention, there is provided a sandwich panel structure comprising a slotted panel and a tabbed panel. The slotted panel includes a slotted panel core body and a first slotted panel facesheet. The slotted panel core body further defines opposing first and second slotted panel sides. The first slotted panel facesheet is disposed adjacent the first slotted panel side and further includes a plurality of first slots formed therethrough.
The tabbed panel includes a tabbed panel core body and a first tabbed panel facesheet. The tabbed panel core body further defines opposing first and second tabbed panel sides, the first tabbed panel facesheet disposed adjacent the first tabbed panel side. The first tabbed panel facesheet further includes a first joint edge and a plurality of first tabs disposed along the first joint edge with each of the first tabs respectively sized and configured to be received by a respective one of the first slots upon insertion of the first tabs into the first slots for joining the tabbed panel to the slotted panel at the first joint edge.
The sandwich panel structure of the present invention differs from existing sandwich panel structures in that the sandwich panel joint configuration of the present invention provides an efficient load path across adjacent sandwich panels. In addition, the sandwich panel joint configuration of the present invention may provide improved heat conduction characteristics across the joint. This is because a tabbed panel facesheet of an interior panel that supports instrumentation may also transfer the heat generated by the instrumentation to the exterior of an adjacent slotted panel.
According to various embodiments, the tabbed panel may be disposed generally perpendicular to the slotted panel. The tabbed panel may further be disposed at an angle from about 45xc2x0 to about 135xc2x0 to the slotted panel. The first tabs may further be aligned and in another embodiment, the first tabs may be bonded to the first slots. The first tabs may extend through at least about 50 percent of a thickness of the slotted panel core body, and in another embodiment the first tabs may extend through at least about 80 percent of a thickness of the slotted panel core body.
The slotted panel may further include a second slotted panel facesheet disposed adjacent the first slotted panel side. The tabbed panel may further include a second tabbed panel facesheet disposed adjacent the second tabbed panel side. The first tabbed panel facesheet may further be constructed of a heat conducting material. The first slotted panel facesheet may be formed of a metal material. The first tabbed panel facesheet may also be formed of a metal material.
The tabbed panel core body may further be formed of a cellular material. The cellular material may further be a honeycomb material. The honeycomb material may further include a plurality of cells, the cells further defining longitudinal axes extending perpendicular to the first and second slotted panel with the first tabs further extending through the first slots parallel to the longitudinal axes of the cells. The orientation of the longitudinal axes of the cells parallel to the first tabs may further aid in the conduction of heat away from the first tabbed panel facesheet to the second slotted panel side. The tabbed panel core body and the slotted panel core body may further be formed of a metal material. The slotted panel core body may further define a slotted panel end and the first slots may further be disposed adjacent to and along the slotted panel end. The tabbed panel core body may further include a second tabbed panel facesheet disposed adjacent the slotted panel end with the first tabs received by the first slots.
The first slotted panel facesheet may further include a plurality of first and second slots and the first and second slots may further be formed through the first slotted panel facesheet and arranged in two generally parallel rows. The tabbed panel may further include a second tabbed panel facesheet and the second tabbed panel facesheet may further by disposed adjacent the second tabbed panel side. The second tabbed panel facesheet may further include a plurality of second tabs disposed respectively along a second joint edge. Each of the second tabs may further be respectively sized and configured to be received by a respective one of the first and second slots upon insertion of the second tabs into the respective second slots for joining the tabbed panel to the slotted panel at the second joint edge.